1. Technical Field
This invention relates to solar battery modules of portable or other types as typified by electronic equipment applications having solar batteries built therein, and more particularly, to solar battery modules serving as photovoltaic devices which when integrated in equipment, provide a harmony of color, and especially of design and have a color not causing an odd sensation despite solar battery mounting.
2. Background Art
Solar batteries are utilized in various electronic equipment as a power supply substitute for dry batteries. In particular, low power consumption electronic equipment such as electronic desktop calculators, watches, and portable electronic equipment (e.g., cameras, cellular phones and commercial radar detectors) can be fully driven by the electromotive force of solar batteries, so that the equipment can operate semi-permanently without a need for battery replacement. Because of the semi-permanent operation combined with cleanness to the environment, solar batteries are of great interest.
When solar batteries are built in electronic equipment, a consideration must be taken from the design aspect. In particular, modern electronic equipment are at an equal performance level imposing difficulty to discriminate one as superior in performance to another and the choice of a product by the consumer often depends on the superiority of design. Because of the structure of the solar battery, the mechanism of the light-receiving surface is visually perceivable from the exterior. Therefore, the design is largely affected by the difference in brightness or color between the photoelectric conversion section having a photoelectric converting function on the light-receiving surface and other regions such as electrodes, isolation walls and other structures. As a general rule, if these structures are viewed from the exterior, most of them have a detrimental effect on the design.
JP-A 60-148174 discloses a solar battery comprising at its front face a selective reflecting layer (multilayer interference filter such as a dichroic mirror) which selectively reflects a portion of visible light having a specific wavelength band, transmits the reminder and transmits at least a portion of light in a wavelength band contributing to the power generation of the solar battery and a light diffusing layer disposed on the front surface of the selective reflecting layer. With this construction, the solar battery exhibiting a dark color becomes the lowermost layer, the "selective reflecting layer" is provided as an upper layer on its light-receiving surface side for changing the color to a color of preference, and a "diffuse transmission layer" is provided as an upper layer thereon for rendering the reflected light brighter for reducing the dark color of the solar battery so that the color is controllable to some extent. This allows for a freedom of design of the color and other factors of the built-in system, thereby mitigating the odd sensation in product design caused by incorporating the solar battery.
The solar battery module that has been used in practice has a photoelectric conversion film capable of producing a photovoltaic force, a transparent electrode, a comb-shaped collector electrode in the form of a conductive silver film formed on the transparent electrode, and a conductive film of Ag, Cu, Ni, Mo or alloys thereof, carbon black or graphitized carbon black serving as a peripheral wiring electrode. The transparent conductive films known in the art include SiO.sub.2 -doped ITO films, SnO.sub.2 films (inclusive of Sb or F doping type), and ZnO films (inclusive of In, Al or Si doping type). Of these, ITO is commonly used. In addition, by forming a multi-stage cell structure capable of producing a desired high voltage on a single substrate, by forming a printed insulating film for patterning necessary for series connection, by effecting laser scribing/patterning by a dry process followed by printing of an insulating resin thereon to form barriers, or by printing conductive ink to form a laser bonding structure, an integrated structure is established (this is more outstanding in the case of a film solar cell which is easy to form into an integrated structure). With respect to the color of the solar battery as viewed from its light-receiving surface, a uniform color surface given by the interference color of the transparent electrode thin film (dictating the majority of the color of the solar battery) which is overlapped by the color of the .alpha.--Si photoelectric conversion film is mixed with patterns of various line widths having optical characteristics including high light reflectance, high light absorbance, high light transmittance and specific wavelength absorption caused by the formation of the above integrated structure, interfering with the color harmony from the design standpoint.
One patterning process is capable of integrating a transparent electrode formed on a substrate by sputtering through a metal mask, a photoelectric conversion film by plasma CVD, and a metal electrode by sputtering together, without using screen printing or laser scribing. Of these components, the metal electrode overlapping the mask shielding area exhibits a high reflectance and provides a high contrast to the photoelectric conversion section within the non-mask shielding area, giving an odd sensation. It is quite difficult to eliminate the odd sensation even when a diffuse transmission layer is formed on top of the cell to provide a shield.
Accordingly, even when the selective reflecting layer and diffuse transmission layer described in the above-referred patent are formed as upper layers on the light-receiving surface side of the solar battery, various pattern lines which are different in brightness, color, reflectance and clearness due to the respective optical characteristics are viewed as being admixed in the uniform color surface and look like a relief. To render these pattern lines to be not perceivable to the view is a key factor in eliminating the odd sensation in product design caused by building in the solar battery although the conventional solar battery design lacked a careful consideration taken to allow for a freedom of product design. In particular, for the "solar watch" in which the movement can be driven by the electromotive force that a solar battery produces at an indoor low illuminance, stringent design requirements are imposed. Further, when a watch dial plate of a color selected from a wide range, though frequently white, serving as a selective reflecting layer and a diffuse transmission layer too is provided as an upper layer on the light-receiving surface side of the solar battery, the gap therebetween should be reduced to a nearly contact state due to the thickness reduction demand. The above requirements should be met even under such service circumstances.
Further, the solar battery module is required to improve the power generation efficiency at a given light source and illuminance, or to form a multi-stage integrated structure to improve the voltage to comply with the requirement of a particular device used, to thereby improve battery performance whereas giving the solar battery-built-in product itself a freedom of design in harmony with the surrounding environment is also a technical task to be solved for the solar battery to find a wider range of market as a clean energy source.